Project Summary Reducing reimbursement levels within a fee-for-service environment is a promising approach for reducing ineffective and unproven care when revoking coverage entirely or shifting financial risk to providers are infeasible. Intensity-modulated radiation therapy (IMRT) was rapidly adopted into practice as a treatment for breast and prostate cancer patients in the early to mid-2000s despite the absence of high quality evidence demonstrating its superiority to conventional radiotherapy. Based on the rising volume of claims for IMRT and a Wall St. Journal article calling attention to the perverse incentives inherent in physician self-referral for IMRT, the Centers for Medicare & Medicaid Services (CMS) cut the payment rate for IMRT by 15% between 2012 and 2013. Using Medicare claims data, we propose to study the impact of the payment cut on the use of IMRT and medical costs. We will study trends in the use of IMRT across three patient groups that differ in their ability to benefit from IMRT: prostate cancer patients receiving initial treatment, prostate cancer patients receiving radiotherapy following prostatectomy, and breast cancer patients receiving radiotherapy following breast conserving surgery. We will use several strategies to accurately estimate the impact of the payment cut. The magnitude of the cut differed across CMS payment areas. We will determine if declines in the use of IMRT were larger in areas that experienced steeper cuts. Separately, we will compare trends in the use of IMRT in three practice settings that differ in terms of the impact of the cut on practice income: self-referring physician offices, non-self-referring physician offices, and hospital outpatient departments (which were unaffected by the cut).